Unveiling the nature of dark matter with direct detection experiments
Doktorsavhandling, 2020

The desire of discovery is an anthropic need which characterises and connects the human being over the eras. In particular, observing the sky is an instinctive drive exerted by the curiosity of the mysteries which it retains. At the present time, the tremendous advances in the exploration of space have opened even more challenges than back in the days. One of the most urgent question is unveiling the nature of dark matter (DM). As stated by Neta A. Bahcall (Professor at Princeton University), "Cosmology has revealed an amazing universe, filled with a "dark sector" that composes 95% of the energy density of our cosmos [...]" (Dark matter universe, PNAS, 2015). About one-third of this dark sector is associated to an invisible and still undetected form of matter, the so-called dark matter, whose gravitational effect manifests at all cosmological scales. Both theoretical and experimental observations based on ordinary gravity reinforced the evidences for the existence of DM, since its first appearance in the pioneering calculations of F. Zwicky (1933). This PhD project explores the hypothesis that DM is made of new particles beyond the standard model. More specifically, it focuses on those DM particles which are trapped into the galactic gravitational field and populate the galactic halo. If DM interacts with ordinary particles, extremely sensitive detectors operating in very low-background environments, are expected to detect galactic DM particles scattering off their target material. This widely employed experimental technique is known as DM direct detection and it is the focus of my studies, where I consider the further hypothesis that DM interacts with atomic nuclei. The research I conducted during my PhD program consists of two main parts: the first part focused on purely phenomenology aspects of the DM direct detection (namely on the DM annual modulation treated using a non-relativistic effective theory and on the scattering of spin-1 DM particles off polarised nuclei) and the second one is more closely connected to experimental applications. The latter has been strongly stimulated by my collaboration with the two DM direct detection experiments CRESST and COSINUS.  For CRESST, I compute the DM-nucleus cross-section for the conventional spin-dependent interactions, used to analyse the data collected with a prototype Li-based detector module, and I derive some prospects for a time dependent analysis of CRESST-III data, using a statistical frequentist approach based on Monte Carlo simulations. For COSINUS, I provide a significant extension of the pulse shape model currently used by CRESST and COSINUS in order to explain experimental observations related to the COSINUS detector response. Finally, I contribute to ongoing studies on the phonon propagation in NaI crystals based on solid state physics. This PhD thesis has been oriented to fill the gap between theoretical and experimental efforts in the DM field. This approach has facilitated the exchange of expertise, has driven the trend of my research and has stimulated the development of the ideas and methods described in this PhD thesis.











Zoom meeting
Opponent: Prof. Nicolao Fornengo, Department of Theoretical Physics, University of Torino and INFN, Italy


Vanessa Zema

Chalmers, Fysik, Subatomär fysik och plasmafysik

Introduction to the Formalism of Neutrino Oscillations

The State of the Art of Neutrino Physics A Tutorial for Graduate Students and Young Researchers,; (2018)p. 37-119

Kapitel i bok

Direct detection of fermionic and vector dark matter with polarised targets

Journal of Cosmology and Astroparticle Physics,; Vol. 2018(2018)

Artikel i vetenskaplig tidskrift

First results on sub-GeV spin-dependent dark matter interactions with Li-7

European Physical Journal C,; Vol. 79(2019)

Artikel i vetenskaplig tidskrift

First results from the CRESST-III low-mass dark matter program

Physical Review D,; Vol. 100(2019)

Artikel i vetenskaplig tidskrift

Cosinus: A NaI-based cryogenic calorimeter for direct dark matter search

Nuovo Cimento della Societa Italiana di Fisica C,; Vol. 42(2019)

Artikel i vetenskaplig tidskrift

COSINUS: Cryogenic Calorimeters for the Direct Dark Matter Search with NaI Crystals

Journal of Low Temperature Physics,; Vol. 200(2020)p. 428-436

Artikel i vetenskaplig tidskrift

Catena, R., Zema, V. Studies for DM signal discovery and model selection via timing information in the CRESST experiment

What is dark matter? Astrophysical and cosmological observations suggest that in the Universe there is a large amount of invisible matter of unknown nature. The mystery is intricate and exciting, and involves several branches of particle physics and astrophysics. It is, indeed, one of the main challenges in the field known as Astroparticle Physics. The goal of my research is to propose ideas that could lead to the discovery of a dark matter signal. In particular, my project consists in developing new methods of analysis of the data collected by the dark matter experiments which adopt the so-called “direct detection technique”. The principle of direct detection is based on measuring the signal produced inside the detectors by dark matter particles, which float in the galaxy and hit the nuclei or the electrons of the detector itself. My work focuses on the dark matter-nucleus scattering phenomenology. One of the ideas I developed in this thesis is to work out how the timing of the signal can be used to extract information on the properties of this hypothetical new kind of particle. Another contribution was to assume specific properties of the dark matter particles, and to compare the resulting shape of the signals obtained in the different cases in order to identify the nature of dark matter. During my PhD I had the great opportunity to closely collaborate with two direct detection experiments, CRESST and COSINUS. These experiments will implement the results of my research, but they are only the first to benefit from them. In particular, I contributed to develop a model, as well as a new analysis method for the COSINUS experiment, which are already going online. Once a detailed validation with data gives a positive outcome, this method has the potential to be implemented also in other experiments with the same working principle as COSINUS.


Subatomär fysik

Astronomi, astrofysik och kosmologi

Den kondenserade materiens fysik



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4821


Chalmers tekniska högskola

Zoom meeting

Opponent: Prof. Nicolao Fornengo, Department of Theoretical Physics, University of Torino and INFN, Italy

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